1. Field of the Invention
The present invention generally relates to reducing particle contamination on semiconductor wafers during plasma processing and, more particularly, to gettering charged particles during plasma processing.
2. Description of the Prior Art
In the manufacture of integrated circuits (ICs), semiconductor wafers of silicon (Si) are subjected to several processes. Some of these processes involve a plasma (e.g., etching, plasma deposition and sputtering). Radio frequency (RF) and DC Glow discharge plasmas, for example, are extensively utilized in the manufacture of ICs. Both electropositive and electronegative gases are used to produce plasmas. Electronegative gases, defined as those having a higher ion density than electron density, such as CF.sub.4, CHF.sub.3, C.sub.12, HBr or O.sub.2, present difficult contamination problems for semiconductor manufacturers.
Contaminating particles ranging in size from tenths of microns to microns are produced or grown in the plasmas. The particles normally have a negative charge, and one growth mechanism is thought to involve negative ions which are trapped in the plasma by plasma sheaths. Plasma sheaths form where the plasma comes in contact with a solid and act as a boundary layer between the plasma and solid surface. The size of the sheath is inversely related to plasma density.
Increasing densities of semiconductor circuits make contamination a serious problem to product reliability and may even be a barrier to achieving theoretically possible higher density circuits. It is therefore necessary to provide a way to reduce particle contamination on semiconductor wafers during plasma processing.